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Chlorination is used in industry for the purification of water; 1gm so

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Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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Chlorination is used in industry for the purification of water; 1gm solution of chlorine will remove half of the germs in 1 liter of water. If water containing less than 0.09% of germs is considered clean, what is the minimum amount of chlorine required to purify 150 liter of water containing 0.3 liter of harmful substances?

A. 1
B. 2
C. 3
D. 4
E. 5

Originally posted by Gau0809 on 01 Jan 2015, 11:04.
Last edited by Gau0809 on 02 Jan 2015, 03:01, edited 2 times in total.
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Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 01 Jan 2015, 12:43
gauriranjekar wrote:
Clorination is used in industry for the purification of water; 1gm solution of chlorine will remove half of the germs in 1 litre of water. If water containing less than 0.09% of germs is considered clean, what is the minimum amount of chlorine required to purify 150 litres of water containing0.03 littres of harmful substances?

A. 1
B. 2
C. 3
D. 4
E. 5


hi, please check the highlighted portion. if it is correct. then we don't need to add any chlorine into the water why ?? 0.09% of 150 =0.135. i.e. the concentration of harmful substances ( germs) must be less than this amount. but the amount of harmful substances present in the water is already less than this amount. hence we don't need to add any chlorine into the water.
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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 01 Jan 2015, 17:53
Hi gauriranjekar,

manpreetsingh86 is correct - the highlighted number must be a typo....

Assuming that it's SUPPOSED to state "0.3" liters of harmful substances, here's how you can answer this question.

First, we have to figure out what .09% of 150 liters is...

1% = .01
.1% = .001
.09% = .0009

So, .0009(150) = .135 liters

We need enough doses of chlorine to get the 0.3 liters down to LESS than .135 liters. Each "dose" of chlorine will remove HALF of the harmful substances...

Start = 0.3 liters
After 1st dose = .15 liters
After 2nd dose = .075 liters

We're now below the .135 liters that we need to be less than.

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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 01 Jan 2015, 22:21
manpreetsingh86 wrote:
gauriranjekar wrote:
Chlorination is used in industry for the purification of water; 1gm solution of chlorine will remove half of the germs in 1 litre of water. If water containing less than 0.09% of germs is considered clean, what is the minimum amount of chlorine required to purify 150 litres of water containing0.03 littres of harmful substances?

A. 1
B. 2
C. 3
D. 4
E. 5


hi, please check the highlighted portion. if it is correct. then we don't need to add any chlorine into the water why ?? 0.09% of 150 =0.135. i.e. the concentration of harmful substances ( germs) must be less than this amount. but the amount of harmful substances present in the water are already less than this amount. hence we don't need to add any chlorine into the water.



Hi...thanks for highlighting.
It was a typo. It is 0.3 and not 0.03!!
I corrected it..
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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 02 Jan 2015, 00:18
gauriranjekar wrote:
Chlorination is used in industry for the purification of water; 1gm solution of chlorine will remove half of the germs in 1 liter of water. If water containing less than 0.09% of germs is considered clean, what is the minimum amount of chlorine required to purify 150 liter of water containing 0.3 liter of harmful substances?

A. 1
B. 2
C. 3
D. 4
E. 5



Are you sure the question you typed is correct? Can you put up a screenshot from the original source? I think the question is ambiguous and options make no sense.

1 gm solution of chlorine removes half the germs in 1 liter of water. 150 liter of water will need 150 gm solution of chlorine to kill half the germs. Currently, the water has .3/150 *100 = .2% harmful substances.
Adding 150 gms of chlorine will make it .1% harmful substances.
Now the issue is that do we need another 150 gms of chlorine solution (which will bring the harmful substances down to .05%) or a small amount which will bring the harmful substance concentration down to 0.09% since we need to find the minimum amount of chlorine solution.

The options 1, 2, 3, 4, 5 are of no help!
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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 02 Jan 2015, 02:56
VeritasPrepKarishma wrote:
gauriranjekar wrote:
Chlorination is used in industry for the purification of water; 1gm solution of chlorine will remove half of the germs in 1 liter of water. If water containing less than 0.09% of germs is considered clean, what is the minimum amount of chlorine required to purify 150 liter of water containing 0.3 liter of harmful substances?

A. 1
B. 2
C. 3
D. 4
E. 5



Are you sure the question you typed is correct? Can you put up a screenshot from the original source? I think the question is ambiguous and options make no sense.

1 gm solution of chlorine removes half the germs in 1 liter of water. 150 liter of water will need 150 gm solution of chlorine to kill half the germs. Currently, the water has .3/150 *100 = .2% harmful substances.
Adding 150 gms of chlorine will make it .1% harmful substances.
Now the issue is that do we need another 150 gms of chlorine solution (which will bring the harmful substances down to .05%) or a small amount which will bring the harmful substance concentration down to 0.09% since we need to find the minimum amount of chlorine solution.

The options 1, 2, 3, 4, 5 are of no help!



Hello

Yes, the question is right. I am attaching the screenshot anyway.
And as per the explanation provided in the question source, that additional one gram is required to bring down the harmful substances to 0.05%.
Hence the answer is 2 grams.
Attachments

File comment: Original source file
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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 02 Jan 2015, 02:59
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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 02 Jan 2015, 05:30
gauriranjekar wrote:
Chlorination is used in industry for the purification of water; 1gm solution of chlorine will remove half of the germs in 1 liter of water. If water containing less than 0.09% of germs is considered clean, what is the minimum amount of chlorine required to purify 150 liter of water containing 0.3 liter of harmful substances?

A. 1
B. 2
C. 3
D. 4
E. 5


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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 02 Jan 2015, 08:07
Is something wrong with the question?
If 1gm solution of chlorine will remove half of the germs in 1 liter of water, then 150 gms of chlorine will be required twice to purify 150 liter of water containing 0.3 liter of harmful substances.
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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 02 Jan 2015, 10:54
Maybe we need to point out what is the minimum amount of chlorine in the solution. That would be 2 gm per liter.
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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 04 Jan 2015, 22:31
gauriranjekar wrote:
Yes, the question is right. I am attaching the screenshot anyway.
And as per the explanation provided in the question source, that additional one gram is required to bring down the harmful substances to 0.05%.
Hence the answer is 2 grams.


Right, but the quantity of water given is 150 liters, not 1 liter. So 150 gms of chlorine solution will bring the harmful substances down to 50% of the original amount. Also, the options do not specify the units of measurement - 1 gm etc.
Something certainly wrong with this question.
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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 31 May 2016, 11:05
Gau0809 wrote:
VeritasPrepKarishma wrote:
gauriranjekar wrote:
Chlorination is used in industry for the purification of water; 1gm solution of chlorine will remove half of the germs in 1 liter of water. If water containing less than 0.09% of germs is considered clean, what is the minimum amount of chlorine required to purify 150 liter of water containing 0.3 liter of harmful substances?

A. 1
B. 2
C. 3
D. 4
E. 5



Are you sure the question you typed is correct? Can you put up a screenshot from the original source? I think the question is ambiguous and options make no sense.

1 gm solution of chlorine removes half the germs in 1 liter of water. 150 liter of water will need 150 gm solution of chlorine to kill half the germs. Currently, the water has .3/150 *100 = .2% harmful substances.
Adding 150 gms of chlorine will make it .1% harmful substances.
Now the issue is that do we need another 150 gms of chlorine solution (which will bring the harmful substances down to .05%) or a small amount which will bring the harmful substance concentration down to 0.09% since we need to find the minimum amount of chlorine solution.

The options 1, 2, 3, 4, 5 are of no help!



Hello

Yes, the question is right. I am attaching the screenshot anyway.
And as per the explanation provided in the question source, that additional one gram is required to bring down the harmful substances to 0.05%.
Hence the answer is 2 grams.

here 1gm of chlorine is removing 50% germs.
So 0.3lts germs in 150 lts water comprises 0.2% germs
so to bring quantity of germs below .09% to be considered good solution we need 1gm chlorine
this 1 gm chlorine remove 50% of .2% germs
means still we have 0.1%germs for which we need another 1 gm of chlorine which again removes 50% of 0.1% germs to 0.05%/
which is obviously <0.09%germs
So total 2gms needed.
Ans B
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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 02 Dec 2017, 01:54
VeritasPrepKarishma wrote:
gauriranjekar wrote:
Yes, the question is right. I am attaching the screenshot anyway.
And as per the explanation provided in the question source, that additional one gram is required to bring down the harmful substances to 0.05%.
Hence the answer is 2 grams.


Right, but the quantity of water given is 150 liters, not 1 liter. So 150 gms of chlorine solution will bring the harmful substances down to 50% of the original amount. Also, the options do not specify the units of measurement - 1 gm etc.
Something certainly wrong with this question.


I agree with you. I think the question must be worded to state that - "1 gram of chlorine cleans half of the impurities from every 1 litre of water". If the question is this, then, the answer would be B.
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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 02 Dec 2017, 15:53
This is a poorly worded question. Can we rephrase the "1gm Chlorine is required to remove half the germs in 1 liter of water"? Or change the answer choices...
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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 18 Dec 2017, 20:40
I am amazed the source is GMAT Prep
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Re: Chlorination is used in industry for the purification of water; 1gm so  [#permalink]

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New post 22 Mar 2018, 12:18
150 litres of water contains 0.3 litres of harmful substances ( i am assuming harmful as germs)
so 1 litre of water contains 0.3/150 litres of germs.

(1/2)^n * 0.3/150 < 0.09/100, where n number of grams of chlorine required.
=> (1/2)^n < 0.45
=> we need minimum of 2 gms of chlorine
Re: Chlorination is used in industry for the purification of water; 1gm so &nbs [#permalink] 22 Mar 2018, 12:18
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